I agree in general, but you are painting with too broad strokes here:

> No part of cryptography has anything to do with the code.

There have been successful attacks against cryptography based on attacking the implementation. For example if two code paths take different time to execute, it is possible that this leaks information.

This is another reason why you should use a well honed library implementation of cryptography, for example OpenSSL.

This does of course not imply that the crypto–the maths of it–is broken. One just needs to be aware that it is not, in fact, sufficient to implement the maths correctly.